In Nitro Nation you can link social accounts, such as Facebook, Google, Apple or Huawei to your in-game profile. If you later link them again, you will automatically log in into your game profile.
If you attempt to link the account in the game settings and the game says that “the account is In use”, it means that this social account is already linked to an existing Nitro Nation profile.
To log in with it and access your Nitro Nation profile, go to the main menu – Garage – Profile. Here tap “Edit/switch profile” and then tap "NEW PLAYER". On the following screen, choose "Sign in with Facebook/Google/Apple/Huawei", that should allow you to choose your FB/Google/Apple/Huawei profile and log in with it.
Important: “Log in with Google” option is available on Android devices only, Huawei - on Huawei devices, Apple ID - on iOS devices, and so on.